Page 1 of 7 123456 ... LastLast
Results 1 to 15 of 100
  1. #1
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    5,974

    Default More metal bluing

    About 3 years ago I set up a small metal bluing tank bluing and posted a few details a a couple of photos in this post.
    My second attempt at steel bluing

    Since then I have blued some small pieces, and have also have received a few PMs about what I do.
    What I have been meaning to do for a while is post a few more details of the process and include some more pics.

    The pieces I am bluing are the bearing housing, wheel collar/flange and table hold down screw for the thin kerf cut off saw I made a couple of weeks back.

    This is the bearing housing before and after bluing - not the best bit of machining but it works and it's done now and that's what I have to work with.
    STart.jpg finalass1.jpg

    The recipe I used was almost identical to what I have posted before but here it is again but this time with pictures.

    List of requirements:
    - 20 -50L acid resistant, well sealable chamber to act as a fume chamber
    - 3 x 1-2L wide mouthed acid resistant, sealable containers
    - Acid resistant suspension rod for inside of chamber.
    - 20-30 ml of each of concentrated hydrochloric acid (HCL ) and nitric acid HNO3.
    - solvent/degreaser for cleaning parts
    - Sodium carbonate (foot bath salts) also
    for cleaning parts
    - Sodium bicarbonate to neutralise discarded acids
    - Distilled water
    - hot plate or ways of heating several litres of distilled water, oil, and sodium carbonate solution.
    - fine steel will 000 and 0000 grade
    - toothbrush size soft steel brushes.
    - acid proof gloves and eye protection to handle acids
    - Latex gloves to handle work parts
    - Separate clean SS saucepans/containers to hold distilled water, oil, and sodium carbonate cleaning solution.
    - wire hooks to suspend parts inside fume chamber. TIG SS filler rod makes good hooks for small parts.

    1) Initial Prep
    Polish the metal to as high a shine as you desire for the final finish.
    The smoother the finish the thinner and more reflective and protective the coating will be.
    Mine have only been polished using a scotchbrite wheel so it was more of a matt polish.
    Sorry no pics of this stage

    2) Cleaning of parts
    Remove as much oil and gunk from the metal parts using an appropriate solvent/degreaser.
    Unless rust is thick and scaly there's no need to remove it - as long as you are happy with the smoothness
    Remove the solvent/degreaser.by boiling parts in a weak (5%) solution of sodium carbonate [(Foot spa salts) a 500g bag costs about $5 a bag at most supermarkets] for an hour.
    You can keep the sodium carbonate solution and reuse it multiple times - it also makes a very good electrolysis solution.
    Waste or spent sodium carbonate solution can be disposed of down normal drains.
    From this point onwards handle the parts with rubber gloves. I use disposable latex types available at supermarkets.

    3) Chamber preparation
    NB: gloves and eye protection is recommended when setting up the acids.
    The exposure chamber needs to be;
    - large enough to hold the pieces but not too small so that the pieces might contact the acids.
    - highly acid resistant and able to be sealed so something like a HDPE drum is ideal.
    - able to be well sealed to keep in the fumes or they will leak and corrode all ferrous stuff they come into contact with outside the chamber.
    - able to hold a suspension rod of some kind high up in the chamber - I use PVC pipe jammed tightly up agains the chamber walls.
    At the bottom of the chamber place two open smaller (~1L) containers one with 20-30mL of concentrated HCl and the other with 20-30mL concentrated HNO3.
    Another container with 20-30mL water can be added if there is room inside the chamber - this increases the moisture content of the air in the chamber and aids rust development.

    4) Loading up the Chamber
    Wet the parts with distilled water and suspend the pieces in the bluing chamber from pieces of wire as shown below.
    Make sure the hooks are strong enough to support the pieces to reduce the chances of them falling into the acid containers below (disaster!).
    On warm-hot days day you can place the sealed chamber containing the parts outside but I would not recommend under direct sunlight.

    You can reuse the small containers containing the acids over and over - depending on how many times you open and close the chamber they can last for many years.
    Over time (hundred or so passes) the acids will produce fewer fumes and may need to be replaced.

    If you are not using the chamber the acid containers should be sealed/closed to prevent los of fumes.
    Used acids should be neutralised and this can be done by careful slow addition of small amounts the acid into an acid proof container (eg plastic bucket) containing a couple of litres of ~50g/L of baking soda solution. Both the acids can be added to the same bucket of neutralising agent. The resulting solution can be safely poured down the sink

    suspense.jpg

    After the parts have formed a coating of rust [this can take anywhere from a couple, to 12 hours depending on the ambient temperature] remove the parts from the from chamber.
    Below is they look like after the 4th pass, after the first pass they come a much brighter orange (i.e. rust)
    4thpass.jpg

    5) Rust Conversion using distilled boiling water
    Place the rusty looking parts into a clean container of fresh, boiling distilled water.
    Make sure the container contains enough water to fully immerse the parts and allow extra for losses while boiling.
    I use a large clean stainless steel saucepan on an old electric frying pan and hook the pieces onto the side of the saucepan.
    Boil for at least 10 minutes (longer for complex shapes and intricate parts) so ALL the rust colour goes completely black.
    You can reuse the water for multiple passes until it goes a dark brown/orange colour, and for the last pass (see below) when fresh water should be used.
    Waste water may be slightly acidic but can still be safely disposed of down normal drains

    Cooking.jpg

    Remove and allow parts to dry - you can hurry the process along with compressed air but as they come out hot they dry quickly
    Below is typically how they look after boiling
    It doesn't matter if they appear patchy, underneath like that grey colour on the large middle piece, it will be a sooty black underneath.
    After-boiling.jpg

    6) Removal of loose black oxide
    Now remove the loose "soot", which is black iron oxide,from all surfaces using a fine stainless wire brush and/or fine steel wool.

    Fine steel wool works well on flat surfaces but brushes will work better on threads and into nooks and crannies.
    The amount of soot that comes off looks like you are taking it all off but that is normal.
    Rub hard enough to achieve a smooth surface but not so hard as to get it back to bare metal.
    This shows the amount of soot that comes off ie quite a bit and make a mess hence the need for gloves.
    Carding.jpg

    After the first pass through the bluing tank the metal might only have changed to a medium grey like this but this is entirely normal .
    firstpass.jpg


    8) Repeating processes
    Repeat steps 3 - 7 until the desired depth of colour and protection is obtained.

    This means somewhere around 8-10 passes.
    If you warm the chamber to 30-40șC everything happens quicker, and as few as 4-5 passes might be sufficient.
    Remember you need to use fresh water for final boiling pass.

    Here's what they are looking like after 5 passes (NB the soot has been removed before the photo was taken)
    5thpass.jpg
    They look nice and black in the photo but more cycles will make a more lustrous, more bluer hued colour that is more protective. This batch is going dark a lot quicker than usual - i think it may be because I have been a lot more careful about keeping things clean, i.e. double rinsing of equipment etc.
    It is interesting to see the pieces slightly change colour hue after every few cycles. first they are slate grey, then dark brownish and then faintly blue and then full on black.
    After 4-5 cycles I usually switch to using superfine steel wool

    9) The Final Oil bath
    Finally immerse and heat the parts in hot (~100șC) oil. I use new engine oil in another stainless steel saucepan on the electric frypan) for a 30 minutes, .
    Remove parts from oil, suspend them above the hot oil so they drip their excess oil back not the oil pot, until cool and wipe off any remaining oil with a soft cloth. For maximum protection the parts should be kept very lightly oiled. If they develop surface rust they can be re-blued in just a couple of passes.
    The oil can be reused indefinitely.

    Thats it.
    The thickness of the final finish is in the <5 micron range so that close fitting parts and fine threads should all go back together again very easily.
    It's a very slow process but the finish is supposed to be one of the more r
    obust of the bluing methods. It's not used much because it is so slow.
    Last edited by BobL; 6th Jul 2020 at 07:33 PM.

  2. #2
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    8,686

    Default

    Hi Bob,
    Thanks for the write up.

    Quote Originally Posted by BobL View Post
    The bluing chamber contains two open containers one with concentrated HCl and the other with concentrated HNO3.
    Is this the sort of thing one can get hold of without to much trouble?

    Stuart

  3. #3
    Join Date
    Jul 2014
    Location
    Alphen aan den Rijn, Netherlands
    Posts
    208

    Default

    Hi Bob,
    Thanks for the explanation. Sounds like something I will try in the future. I have a couple of questions if you don't mind:
    Why heating in oil for so long? Isn't it enough if the formed layer is saturated with oil (and the heating to make it more "liquid" and "wet" better?)
    I use the water that accumulates in the dryer when we dry our clothes as distilled water. Would that be good enough for this application? (might contain a little pocket fluff ;-) )
    In your previous post you also mentioned another acid that could be used. Is there any difference in application or result?

    Thanks
    Peter.

  4. #4
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    5,974

    Default

    Quote Originally Posted by Stustoys View Post
    Hi Bob,
    Thanks for the write up.

    Is this the sort of thing one can get hold of without to much trouble?

    Stuart
    For Concentrated HCl I used Diggers Spiirts of Salts from Bunnings.
    Nitric acid is not so easy to get but Sulphuric acid can be substituted for nitric..

    Diluter forms will also work but take longer although some reduction in time can be achieved by then using a smaller chamber/

  5. #5
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    5,974

    Default

    Quote Originally Posted by WoodBee2 View Post
    Hi Bob,
    Thanks for the explanation. Sounds like something I will try in the future. I have a couple of questions if you don't mind:
    Why heating in oil for so long? Isn't it enough if the formed layer is saturated with oil (and the heating to make it more "liquid" and "wet" better?)
    I would not be heating the coated object with something like a flame and then dunking it it oil as that may form a coating of scale and polymerised oil which ruins the finish and will interfere with any fine fitting required. The major benefit of this type of finish is that it is very thin which means machined parts will easily go back together again.
    If I don't need the fine fit or finish and just want rust protection then because it takes so long I wouldn't bother to blue the metal and heating and dunk in oil .

    The length of time in the hot oil was in the recipe I got from Guy Leotards book.
    I reckon one could get away with a shorter time than an hour but as far as I can I have stuck to his recipe.

    I use the water that accumulates in the dryer when we dry our clothes as distilled water. Would that be good enough for this application? (might contain a little pocket fluff ;-)
    As long as the water accumulator container is clean, no bugs or moulds etc. While the fluff will contain some impurities this water should be better than any tap water and should work OK.
    The cleaner and purer everything is the stronger the coating.
    Because of the cleaning requirements and the number of passes needed to get a good coating the amount of distilled water needed is quite high (I go though about 40L to do a batch) and this can be expensive if you need to buy it. The volume of water could be scaled back considerably by using a smaller saucepan

    In your previous post you also mentioned another acid that could be used. Is there any difference in application or result?
    Yes sulphuric acid - sometimes found in brick cleaners - can be used. There is no difference in the way it is done or the end result except that concentrated Sulphuric acid probably smells worse than the other

  6. #6
    Join Date
    Jun 2013
    Location
    Tasmania
    Posts
    244

    Default

    This technique is called rust bluing and has been used on firearms for 100+years. Pretty easy to do as you say, just labour intensive.

    I use a wipe on solution of a mix of hydrochloric acid (battery acid), nitric acid and iron filing and distilled water. The technique you use is called fuming.

    The mix I use is 20ml Nitric Acid (I think its about 68% conc), 13ml hydrochloric acid (30% conc) and then keep adding iron filing until the solution stops reacting then add the ACID TO THE WATER (160mls of water). Makes about 200mls, store it and protect from light. Hazardous note: Adding the iron to the acid produces a bubbling reaction, heat, and puts off brown nitrogen dioxide gas which is not good for you. Best done in a fume hood, but I guess you could just try running away.

    Polish your parts (no need to go above 320grit really). Then degrease well, and from this point on handle only with gloves:


    Wipe on a very thin layer of the acid mix, just enough to wet the part. Put them in a humid environment and let them rust (usually overnight):




    Dont let them rust too long or the parts will pit. Just enough to get a brown dust on them. The above pics are probably a bit too far, but I repolished and started again on one of them. The other part was saved. Boil in distilled or deionised water (can get 2 litres from the supermarket in the ironing section for about a $1.50) until the part turns black. I reuse the water a few times, so for small parts I only need maybe 4L total for the whole job. You just need enough to cover the parts while boiling.

    Pull them out and blow the water off with the air compressor to stop more flash rusting. The rub down with a fine carding wheel (from Brownells) or DEGREASED 0000 steel wool.

    Repeat.

    Produces a pretty nice and durable finish if you ask me







  7. #7
    Join Date
    Nov 2008
    Location
    Perth WA
    Age
    68
    Posts
    6,284

    Default

    Now Bob and Hornet,

    How about a recipe for blackening brass?

    Bob.

    PS Hornet, any chance of expanding a bit on the "humid environment"?

  8. #8
    Join Date
    Jul 2010
    Location
    Melbourne
    Posts
    8,686

    Default

    Hi Hornet,

    Is it normal to do the red dot first?
    Do you recall how many "repeats" there were?

    Stuart

  9. #9
    Join Date
    Jun 2013
    Location
    Tasmania
    Posts
    244

    Default

    Quote Originally Posted by Anorak Bob View Post
    Now Bob and Hornet,

    How about a recipe for blackening brass?

    Bob.

    PS Hornet, any chance of expanding a bit on the "humid environment"?

    I haven't blackened any brass sorry, but it seems that sulphur is a favourable component to achieving this. In fact Birchwood Casey makes a Brass Black solution. I have no idea if it works well or not, as their cold blues are terrible in my experience. I often find recipes for doing these sorts of things from www.finishing.com

    http://www.finishing.com/1000-1199/1198.shtml

    Birchwood casey comments:
    http://www.modelboatyard.com/blackening.html

    http://www.traditionalfisherman.com/...hp?f=50&t=8482

    The humid environment I use is a plastic box (or my long thin boiling tank with a lid on if it's a gun barrel) in which I put a slightly damp piece of rag in overnight. Works better if the temperature isn't freezing but if you had somewhere that was a little warm it would be best. I have seen others use a low wattage light bulb to raise the temp slightly and make a warm humid environment. The warmer and more humid the faster it rusts, which depending on your work schedule may or may not work in your favour. If you have it too wet or there are too big a temperature swings you get larger droplets condensing on the steel that can make the rust uneven. It just depends on how important your finish needs to be. On a rifle, I try to make it impecable. But generally, just leaving it works just fine. And to be honest, I could probably just leave it in my shed with all my machine tools, as they seem to try and rust just fine

    In terms of prebought solutions, Birchwood Casey's Plum Brown works well as a rusting solution also (that's all the browning is, neutralised rust). Just boil the part to turn it black (converts the rust from a red oxide to a black oxide). I've got some of this solution but never used it in this fashion, so can't relate first hand experience.

  10. #10
    Join Date
    Jun 2013
    Location
    Tasmania
    Posts
    244

    Default

    Quote Originally Posted by Stustoys View Post
    Hi Hornet,

    Is it normal to do the red dot first?
    Do you recall how many "repeats" there were?

    Stuart
    That was actually the factory red dot. If it wore off I was just going to dot it on again at the end with red automotive acrylic lacquer that I had handy, but I didn't need to. It stayed put just fine.

    Repeats on this piece was probably 8-10 cycles. It varies on different parts, and also the depth of colour can vary depending on the exact steel make up. Some goes nice and black, others a smokey gray. I don't know what determines it though or what exact alloys will give what finish. The steel make up on rifles is already chosen.

    You will see over the number of cycles that the rust gets less and less (which is exactly what you want and gives it its rust resistant properties). As the exposed sites susseptible to rust get occupied by the black oxide (I think it is ferric or ferrous oxide, ones red the other is black), then there are less sites available to rust next time round.

    At some point you decide to stop, it can be handy sometimes to soak it in a gentle alkaline solution like sodium bicarb just to neutralise any residual acid, then as Bob says, soak it in water displacing oil or just oil. I don't heat it but you can I guess.

  11. #11
    Join Date
    Nov 2008
    Location
    Perth WA
    Age
    68
    Posts
    6,284

    Default

    Thank you Hornet,

    I have tried Birchwood Casey's Brass Black but the results were disappointing hence the question - http://www.woodworkforums.com/showth...11#post1813411

    Bob.

  12. #12
    Join Date
    Jun 2013
    Location
    Tasmania
    Posts
    244

    Default

    Quote Originally Posted by Anorak Bob View Post
    Thank you Hornet,

    I have tried Birchwood Casey's Brass Black but the results were disappointing hence the question - http://www.woodworkforums.com/showth...11#post1813411

    Bob.
    Ah Ok.

    Sorry it didn't work out for you. As I alluded to, generally I've found Birchwood Caseys stuff works crap to the point of being misleading and falsely represented. The truoil is ok though, but is a lacquer/varnish more than an oil. The cold blues are pretty pathetic.

    However, I will say from your post that metho is crap as a degreaser, not sure if that is the cause of your poor results. Acetone far out performs it, and at a pinch lacquer thinners also works ok. Just use the acetone in a well ventilated area. Generally these sorts of things rely on impeccable cleanliness and degreasing.

    Another thing I have observed is that generally ANY advise that comes over the counter of a gun shop is worth about 5/8th of FA.

    If you find something that works I'd be interested to hear also. And like you, I've found it difficult to source straight ammonia.

  13. #13
    BobL is offline Member: Blue and white apron brigade
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    5,974

    Default

    Quote Originally Posted by Hornetb View Post
    However, I will say from your post that metho is crap as a degreaser, not sure if that is the cause of your poor results. Acetone far out performs it, and at a pinch lacquer thinners also works ok. Just use the acetone in a well ventilated area. Generally these sorts of things rely on impeccable cleanliness and degreasing..
    I agree about metho being a poor degreaser. The way it is made is not that clean. Isopropyl alcohol can be obtained in a fairly pure state and is in some ways a better cleaner and it is also safer than acetone. The best degreaser I've found is dichorlomethane but that can be quite hard to get. I have access to all these chemicals but my preference is for IPA simply because I can now get a lot of it.

    If you find something that works I'd be interested to hear also. And like you, I've found it difficult to source straight ammonia.
    It's quite easy to make pure ammonia from cloudy ammonia by room temperature vapour transfer.
    To do this you need a way of connecting two PE bottle necks together so that it is as gas tight as possible. (black poly elbow and fittings plus heap of teflon tape usually does it).
    Completely gas tight is bad as it may then explode. In one bottle place some distilled water and wrap that bottle in al-foil inside an oven bag.

    In the other bottle place some cloudy ammonia and warm that side using an incandescent light globe dangled above the cloudy ammonia container or just leave it for a week.
    Eventually the NH3 concentration will equilibrate between both sides.
    Repeatedly changing the source will slowly increase the concentration of the NH3 in the receiver.
    I have managed to get the water very close to the ammonia concentration in the cloudy ammonia side using this method

    Pull them out and blow the water off with the air compressor to stop more flash rusting. The rub down with a fine carding wheel (from Brownells) or DEGREASED 0000 steel wool.
    A source of oil contamination I found was air from the compressor so the only time I use the compressor is at the end of the last rust stage.
    I just let them air dry when I pull them out of the boiling water as I found it doesn't matter if they develop a bit of rust in the middle of the rusting cycles as this will be converted in the next cycle anyway.
    Attached Images Attached Images

  14. #14
    Join Date
    Nov 2008
    Location
    Perth WA
    Age
    68
    Posts
    6,284

    Default

    Thanks Bob,

    Back when you initially described the process, I had looked online for some laboratory fittings thinking that was the easiest route and then I asked my daughter's boyfriend if he could scrounge some ammonia from his father's industrial cleaning products factory. The Melbourne - Perth thing made it all too hard and that idea fizzed out. Your diagram makes it look very simple. I'm enthused again.

    How about this for isopropyl alcohol? - http://shop.coles.com.au/online/nati...ubbing-alcohol

    BT

  15. #15
    Join Date
    Jun 2013
    Location
    Tasmania
    Posts
    244

    Default

    Quote Originally Posted by BobL View Post
    A source of oil contamination I found was air from the compressor so the only time I use the compressor is at the end of the last rust stage.
    I just let them air dry when I pull them out of the boiling water as I found it doesn't matter if they develop a bit of rust in the middle of the rusting cycles as this will be converted in the next cycle anyway.
    Yes, that is a fair point. Contamination is your enemy. To be honest I have probably only done that more towards the end of the process.

    When I actually blow with compressed air it is usually when I'm doing a rifle barrel and I do it mainly to clear water from the rifle bore as that is my biggest concern with rust and I dont want that rusting at all. A lot of people plug the ends of the barrel with wooden dowels to keep the water out, but I'm nervous to leave it locked up for the week it takes to blue. You can coat the bore with lacquer and then use lacquer thinner to clean it out at the end too. This of course relates mainly to firearms.

    I do plan to set up a hot bluing set up, but this is another level of danger with boiling hot sodium hydroxide and potassium nitrate just for added fun. But the process is much quicker and easier, but the consequences a lot nastier.

Page 1 of 7 123456 ... LastLast

Similar Threads

  1. My second attempt at steel bluing
    By BobL in forum METALWORK GENERAL
    Replies: 20
    Last Post: 4th Dec 2018, 02:25 PM
  2. Blacking As An Alternative to Bluing
    By Anorak Bob in forum METALWORK GENERAL
    Replies: 7
    Last Post: 6th Jan 2014, 08:32 AM
  3. Bluing a tapered shaft
    By jack620 in forum METALWORK GENERAL
    Replies: 20
    Last Post: 9th Apr 2013, 07:02 PM
  4. Bluing
    By bollie7 in forum METALWORK GENERAL
    Replies: 1
    Last Post: 28th Apr 2009, 10:37 PM
  5. Metal bluing solution
    By ohno in forum METALWORK GENERAL
    Replies: 28
    Last Post: 16th Dec 2006, 08:00 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •